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Osteocyte-Mediated Translation of
Mechanical Stimuli to Cellular Signaling
and Its Role in Bone and Non-bone-
Related Clinical Complications
AQ1
Yongyong Yan,
Liping Wang,
Linhu Ge,
Email 13922177779@163.com
Janak L. Pathak,
Email janakpathak@163.com
Key Laboratory of Oral Medicine, Guangzhou Institute of Oral
Disease,Affiliated Stomatology Hospital of Guangzhou Medical
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University,Guangzhou,510140 China
Abstract
Purpose of Review
Osteocytes comprise >!95% of the cellular component in bone tissue and
produce a wide range of cytokines and cellular signaling molecules in response
to mechanical stimuli. In this review, we aimed to summarize the molecular
mechanisms involved in the osteocyte-mediated translation of mechanical
stimuli to cellular signaling, and discuss their role in skeletal (bone) diseases
and extra-skeletal (non-bone) clinical complications.
Recent Findings
Two decades before, osteocytes were assumed as a dormant cells buried in bone
matrix. In recent years, emerging evidences have shown that osteocytes are
pivotal not only for bone homeostasis but also for vital organ functions such as
muscle, kidney, and heart. Osteocyte mechanotransduction regulates osteoblast
and osteoclast function and maintains bone homeostasis. Mechanical stimuli
modulate the release of osteocyte-derived cytokines, signaling molecules, and
extracellular cellular vesicles that regulate not only the surrounding bone cell
function and bone homeostasis but also the distant organ function in a paracrine
and endocrine fashion.
Summary
Mechanical loading and unloading modulate the osteocytic release of NO,
PGE , and ATPs that regulates multiple cellular signaling such as Wnt/β-
catenin, RANKL/OPG, BMPs, PTH, IGF1, VEGF, sclerostin, and others.
Therefore, the in-depth study of the molecular mechanism of osteocyte
mechanotransduction could unravel therapeutic targets for various bone and
non-bone-related clinical complications such as osteoporosis, sarcopenia, and
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cancer metastasis to bone.
Keywords
Osteocytes
Mechanotransduction
Cellular signaling
Bone homeostasis
This article is part of the Topical Collection on Osteocytes
Liping Wang and Yongyong Yan contributed equally to this study and shared the
first authorship
Introduction
Regular physical exercises such as running, cycling, or other various sports give
mechanical stimuli to the bone and help to maintain healthy and strong bone. In
contrast, mechanical unloading conditions such as long-term bed rest or long-term
space traveling (in the case of astronauts) cause severe bone loss [1–4].
Mechanical loading in physiological range gives an anabolic effect to bone mass,
but in supraphysiological range causes bone loss [5, 6]. Osteocytes are mainly
responsible for the loading-induced anabolic effect on bone. Mechanosensitive
osteocytes comprise 95% of the total bone cell population. Bone cell
mechanotransduction is a complex process regulated by multiple signaling
pathways. Osteocytes reside in lacunar space inside the hard-mineralized bone
matrix. The osteocyte cell body has further 50–60 extensions (cell processes)
originate from lacunae and radiate through the mineralized matrix surrounding the
osteocyte via canaliculi space. This complex structure around the osteocytes is
called lacuno-canalicular system. The osteocyte processes are connected to the
surrounding osteocyte processes and also with the bone lining osteoblasts and
other cells from the bone marrow. Osteocytes play a vital role in bone homeostasis
by regulating osteoblast and osteoclast formation and activity [7–9]. Osteocytes
control osteoclast formation, survival, and activity via the production of receptor
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activator of nuclear factor kappa-Β ligand (RANKL) [10, 11]. Similarly, osteocytes
regulate osteoblast differentiation via activation of Wnt/β-catenin signaling [12,
13]. Furthermore, osteocytes are a major source of sclerostin, a potent inhibitor of
Wnt/β-catenin signaling [14]. Osteocytes play a vital role in bone homeostasis, and
disrupted osteocyte function causes various bone diseases such as osteoporosis,
sclerosteosis, and van Buchem disease (VBD) [15–17]. In addition, osteocytes
have endocrine functions and regulate extra-skeletal (non-bone) functions, such as
phosphate and calcium homeostasis, kidney function, and cardiovascular activities
[18–23]. And disruption of osteocyte functions causes various non-bone clinical
complications [22, 23]. These non-bone clinical complications also affect bone cell
functions and bone homeostasis. PTHR1 signaling in osteocyte plays a crucial role
in bone and non-bone-related complications [8]. Osteocyte-specific proteins
E11/gp38, phosphate-regulating neutral endopeptidase on chromosome X,
sclerostin, dentin matrix protein 1 (DMP1), matrix extracellular
phosphoglycoprotein (MEPE), and fibroblast growth factor-23 influence various
bone cell activity and non-bone systemic diseases such as periodontitis, chronic
kidney disease, cardiac disease, etc.
Mechanical loading of osteocytes not only regulates osteoblast and osteoclast
function and activity but also facilitates osteocyte survival. Mechanical loading of
osteocytes induces activation of osteocyte autophagy and promotes ATP
metabolism in osteocytes. Mechanical loading-induced osteocyte autophagy is
beneficial for osteocyte survival [24]. It has been widely accepted that osteocytes
sense mechanical stimuli and generate cellular signaling to regulate osteoblast and
osteoclast function. However, the molecular mechanism of translation of
mechanical forces to cellular signaling is still not fully understood. The most
accepted mechanism of mechanosensing by osteocyte is loading-induced
interstitial fluid flow in the lacuna-canalicular system. Osteocyte processes sense
interstitial fluid flow and initiate osteocytic cellular signaling [25••]. This
interstitial fluid flow activates the osteocytes to produce a wide range of signaling
molecules regulating the activity of surrounding bone cells as well as distant none
bone cells [26, 27]. Pieces of literature also reported that the osteocyte cell body is
able to sense mechanical stimuli directly [28]. Osteoblast, the precursor of
osteocyte, lacks cell processes and also senses mechanical stimuli to some extent
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[29–31]. In this paper, we review the various molecular mechanisms of osteocyte-
mediated translation of mechanical stimuli to cellular signaling. We further discuss
the role of these cellular signaling in bone and non-bone-related clinical
complications.
Translation of Mechanical Stimuli to Cellular
Signaling
Calcium Ion Oscillation in Osteocytes
A number of studies have shown that mechanical loading of osteocytes increases
intracellular calcium concentration ([Ca ] [32–38], which triggers to generate the
range of cellular signaling. Mechanical loading-induced Ca oscillation in
osteocytes is more pronounced compared to in osteoblasts [35, 39]. This might be
due to unique cell processes in the osteocytes. Hung et al. reported that Influx of
extracellular calcium as well as inositol triphosphate (IP3)-induced calcium release
from intracellular stores is required for generating intracellular calcium response
to flow in bone cells [40]. Lewis et al. investigated the role of osteocyte Ca
signaling in mechanotransduction in vivo [38••]. They created an osteocyte-
targeted genetically encoded Ca indicator mouse model and a bone loading
system in live mice to simultaneously observe the intracellular Ca responses of
individual osteocytes with multiphoton microscopy. The increased number of
responding osteocytes correlated with the applied strain magnitude, but the Ca
intensity within responding osteocytes did not change significantly with
physiological loading magnitudes [38••]. The αVβ3 integrin in cell processes plays
a vital role to sense mechanical stimuli and translate it to chemical signaling
[41–43]. Fluid flow shear stress acts on αVβ3 integrin adhesion sites on the
osteocyte cell process triggering Ca responses that spread towards osteocyte cell
body and triggers Ca signaling [25]. Brown et al. reported that T-type voltage-
sensitive calcium channels mediate mechanically induced calcium oscillations in
osteocytes by regulating endoplasmic reticulum calcium dynamics [44]. The β3
integrin foci on the osteocyte co-localize with the ATP-releasing Panx1 channel,
the P2X7R channel complex, and the T-type CaV3 calcium channel and form a
transduction complex “osteocyte mechanosome” [43]. Interestingly, mechanical
loading-induced Ca oscillation in osteocytes has been reported to release
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extracellular vesicles with bone-regenerative potency [45••].
The mechanical stimuli sense in the cell processes transfers to the cell body via
ATP. The ATP amplifies spread of Ca signaling from cell processes to cell body
and from one osteocyte to another osteocyte network [41]. However, some
literature had reported the involvement of both ATP and gap junction in
mechanical loading-induced intercellular signaling throughout the networks [39,
46••, 47]. Bivi et al. showed the negative role of osteocytic connexin43 (Cx43)
network in the response of bone to mechanical loading [48••]. Osteocyte-specific
knockout of Cx43 in mice increases osteocytic β-catenin expression and enhances
mechanical loading-mediated periosteal bone formation in ulnae [48••]. Dynamic
fluid flow frequency-dependent Ca oscillation has been observed in osteocytes
both in vitro [40] and in situ [36]. Crosstalk between Wnt/β-catenin signaling and
Ca oscillation in osteocytes gives an anabolic effect in bone during mechanical
loading-induced bone fluid flow [36]. In rat vertebral cancellous bone, the
mechanical loading-induced bone formation does not correlate with osteocyte
population, suggesting a possible role of osteocyte connectivity, lacuno-canalicular
nano-geometry, and/or fluid pressure/shear distributions within the marrow space
[49]. Endogenous sphingosine-1-phosphate (S1P) has been reported to facilitate
intracellular calcium response during mechanical loading [50]. Calcium oscillation
in osteocytes triggers the release of downstream signaling molecules such as nitric
oxide (NO) [51–53], prostaglandin E (PGE ) [54], MEPE, insulin-like growth
factor-1 (IGF-1) [55], and β-catenin [56]. These signaling molecules play a crucial
role in bone cell function.
Primary Cilia-Mediated Mechanosensing
Primary cilia are single, non-motile, organelles that extend from the most of the
embryonic and differentiated mammalian cells. Each primary cilium grows above
the basal body derived from the centriole of mother cells after the cell division.
Primary cilia are vital regulators for the transduction of cell signaling pathways
involved in the development and tissue homeostasis [57]. Defective primary ciliary
functions are the leading cause of developmental disorder, i.e., ciliopathies and
many other human diseases [58]. Primary, cilia transduce a wide range of
extracellular signal to cellular responses via various signaling pathways such as
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Hedgehog, Wnt, and platelet-derived growth factor [59, 60]. Malone and
colleagues have reported that fluid flow shear stress deflects primary cilia of bone
cell surface and translates shear force to cellular signaling independently of Ca
flux and stretch-activated ion channels [30], suggesting primary cilia as a part of a
comprehensive array of sensory tools that allow bone cells to maintain bone
homeostasis. Later on, Delling and colleagues reconfirmed the calcium-
independent mechanoresponsive property of primary cilia [61••]. Treatment of
chloral hydrate or gene silencing by IFT88/Polaris siRNA-mediated reduction of
ciliary number in osteoblasts reduce Opn gene expression and PEG2 release [30].
However, the exact mechanism of primary cilia-mediated translation of mechanical
stimuli to cell responses is still not fully understood.
Primary cilia in osteoblasts play an essential role in mechanical loading-induced
matrix mineralization [62]. Osteocyte-specific deletion of a ciliary protein Pkd1
(Pkd1 ) results in impaired sensory function and disrupts mechanical
loading-mediated bone homeostasis [63]. Conditional disruption of Pkd1 in
osteoblasts impairs bone formation resulting in osteopenia [64]. Similarly,
osteoblast-specific deletion of another ciliary protein Kif3a disrupts primary cilia
formation, inhibits bone formation [65, 66], and impairs mechanoresponse [67].
Strategies that can increase the number of primary cilia in osteoblast lineage cells,
including osteocytes or enhance the mechanoresponse of primary cilia, could be
the novel therapeutic approach to treat osteoporosis or clinical problems with
impaired bone regeneration. However, further studies, unraveling the molecular
mechanisms involved in cilia-mediated translation to mechanical stimuli to cellular
response, are essential to establish this hypothesis.
Focal Adhesions-Mediated Mechanosensing
Multiple actin-associated proteins such as paxillin, vinculin, integrin, and talin are
the components of focal adhesions that are involved in conveying the physical
forces to neighboring cells [68–71]. Focal adhesion kinase (FAK) is major
downstream signaling of focal adhesions-mediated mechanosensation [72–75].
FAK is essential for mechanotransduction in both osteocytes and osteoblasts [75,
76]. Zhang and colleagues reported that the osteocyte cell body could directly
sense mechanical stimuli via paxillin transduction [28]. Other focal adhesion
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proteins vinculin, fibronectin, and Cx43 are involved in paxillin-mediated
osteocyte mechanoresponse [28]. Integrins are the heterodimeric transmembrane
protein that contains α and β subunits. Activation of integrins from low-affinity
state to high-affinity state initiates the formation of focal adhesions [77]. α β
integrins play a crucial role in osteocyte mechanotransduction [42, 43, 78–80]. The
higher amount of αvβ3 integrins are present in osteocyte cell processes in
comparison to the cell body [81]. Thi and colleagues have demonstrated the
essential role of αvβ3 integrin osteocyte polarized mechanosensing and
mechanotransduction [25]. Blocking of αVβ3 in MLO-Y4 osteocytes disrupts focal
adhesion assembly and abrogates Cox-2 expression in response to fluid flow [80].
Pavalko and colleagues proposed a “mechanosome complex” hypothesis to explain
how mechanical signals detected through adhesion complexes at the bone cell
membrane are converted into changes in transcription of target genes [82]. This
complex consists of NO, cGMP, protein kinase GII, SHP1, and SHP2 that associate
with β3 integrins through Src and regulate gene expression in response to fluid
flow in bone cells. The above mentioned in vitro studies showed the essential role
of FAK or proteins associated with FAK on osteocyte mechanotransduction. In
contrast, Sato and colleagues recently reported that FAK signaling in osteocytes is
not required for mechanical loading-induced bone regeneration [83••]. Similar
bone phenotype and mechanical loading-mediated bone anabolic effect were
observed in osteocyte-specific FAK knockout mice (FAK ) and FAK mice
[83••]. More in vivo studies are needed to clarify this discrepancy in the role of
osteocyte-specific FAK in mechanotransduction and bone homeostasis.
Osteocyte Mechanoresponse-Mediated Cellular Signaling
Nitric Oxide, Prostaglandin E2, and ATP
NO, prostaglandin, and ATP are the earliest signals released by shear-stressed
osteocytes. Blocking one of the three signals inhibits loading-induced bone
anabolic response [18]. Numbers of studies have demonstrated that mechanical
stimulation of osteocytes enhances NO production [5, 84–88]. Inhibition of NO
production hindered mechanical loading-induced bone formation in rats [84, 85].
Delgado-Calle et al. reported NO as the key regulator of the mechanical loading-
mediated suppression of SOST mRNA expression in osteocytes [89]. Pulsating
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fluid flow (PFF) significantly downregulates the SOST expression in osteocytes,
and NO synthase inhibitor prevents the effect of PFF on osteocytic SOST
expression [89]. Moreover, NO released from osteocytes or osteoblast lineage cells
modulates osteoblast and osteoclast activity exerting an anabolic effect on bone
[86••, 87]. Mechanically loaded osteocytes release PGE to regulate bone
homeostasis [54, 86••, 90]. Cyclooxygenase 2 (Cox-2) is the key enzyme involved
in PGE production [91, 92]. PGE facilitate gap junction function in osteocytes
via paracrine effect [93]. Major gap junction protein connexin43 enhances
PGE dependent activation of β-catenin signaling in bone cells [94]. Similarly,
exogenous sphingosine-1-phosphate (S1P) upregulation has been reported to
regulate PGE release in both unloaded and loaded osteocytes. S1P receptor
regulates mechanical loading-mediated PGE synthesis and releases [50].
Furthermore, S1P regulates the effect of mechanical loading on RANKL/OPG
expression in osteocytes. ATP is a source of direct cellular energy and a potent
signaling molecule responsible for numerous cellular activities. Osteocyte rapidly
releases ATP in response to mechanical stimulation, and the release corresponds
with loading magnitude and duration [24, 47, 95].
Wnt/β-Catenin Signaling
Wnt/β-catenin signaling plays a vital role in bone integrity, osteocyte viability,
osteocyte signaling to other bone cells, and in bone response to loading [96••, 97].
The osteocyte is the major regulator of the anabolic effect of Wnt/β-catenin
signaling in bone [12]. Mechanical loading via cyclic compressive strain has a
potential to enhance osteoblast differentiation via activation of Wnt/β-catenin
signaling pathway [41]. Both in vivo and in vitro mechanical loading models have
revealed that the rapid activation of osteocytic β-catenin in response to load is an
early release of prostaglandin-mediated [98•]. This indicates a key role of PGE in
mechanical loading-mediated bone homeostasis. Santos and colleagues have
reported that fluid flow-induced mechanical loading activates the beta-catenin
signaling pathway in MLO-Y4 osteocytes by a mechanism involving nitric oxide,
focal adhesion kinase, and the Akt signaling pathway [74]. Wnt co-receptor low-
density lipoprotein-related receptor 5 (LRP5) is essential for skeletal
mechanotransduction [96, 99, 100]. Mechanical loading-induced bone formation is
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reduced in LRP knockout (LRP5 ) mice [99, 100]. Similar results have been
reported in the mice with osteocyte-specific LRP5 deletion [101]. This suggests
the essential role of Wnt/β-catenin signaling in osteocyte-mediated
mechanotransduction.
Sclerostin-Related Signaling
Sclerostin, a potent Wnt inhibitor encoded by SOST gene in human, is highly
expressed by mature osteocytes and regulates bone adaptive response to
mechanical loading. Recombinant sclerostin has been reported to attenuate the
effect of mechanical loading on bone via a direct effect on osteocytes [102].
Downregulation of sclerostin in osteocytes is a mandatory step in the
mechanotransduction cascade to activate Wnt signaling and direct osteogenesis
[13]. Mechanical loading reduces Sost/sclerostin levels in rodent ulna, and the
reduction correlates with tissue strain distributions and bone regeneration
indicating the role of Wnt/signaling in mechanically induced bone formation
[103]. Loading-induced osteocytic inhibition of sclerostin promotes bone
formation via alleviating inhibition of Wnt signaling in osteoblasts and also
regulating OPG-mediated suppression of osteoclast activity [103]. Unloading
upregulates osteocytic sclerostin expression that inhibits Wnt signaling and causes
bone loss. A study using Sost knockout mice has revealed that sclerostin
deficiency rescues unloading-induced bone loss [104]. Similarly, sclerostin
deficiency robustly enhances loading-induced bone formation [104]. Due to the
catabolic effect of sclerostin in bone, anti-sclerostin antibodies are developed to
treat bone loss and osteoporosis [105]. Mechanical loading of osteocytes is a
physiological inhibitor of sclerostin, and therefore could be a potential therapeutic
approach in bone degenerative conditions.
Parathyroid Hormone Signaling
Low calcium circulating level triggers parathyroid hormone (PTH) secretion by
parathyroid glands. Chronic elevation in circulating PTH, as in severe primary
hyperthyroidism, secondary hyperparathyroidism, chronic kidney disease, and
calcium deficiency, causes a catabolic effect on bone [106, 107]. Intermittently,
increase in PTH level, as achieved by daily PTH injection, has an anabolic effect
−/−
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on bone [108]. Mechanical loading and/or PTH therapy give anabolic effect on
bone via Pthr1 signaling in osteocytes [8]. Interestingly, increased PTH serum
level was observed in adult men in response to acute exercise [109]. Mechanical
loading-based adaptation in bone tissue composition is localized around individual
osteocytes, and PTH signaling contributes to this adaptation [110]. Similarly, PTH-
related protein-derived peptides (PTHrP peptides) crosstalk with mechanical
signaling pathway to inhibit osteocyte apoptosis and restore bone mass in diabetic
mice [111]. PTHrP protects microgravity-induced osteoblast apoptosis in rodents
[112]. Mechanical stimulation enhances parathyroid hormone type 1 receptor
expression in MLO-Y4 osteocyte plasma membrane [113••]. Exogenous PTHrP
has been reported to add anabolic effect with mechanical loading on diabetic
mouse bone [111]. Findings from the literature indicate a vital role of osteocyte
mechanotransduction-mediated PTH signaling in bone homeostasis.
RANKL/OPG Signaling
RANKL is another key signaling molecule that regulates bone homeostasis by
activating osteoclast formation and activity. Osteoblast lineage cells, including
osteocytes, are the main source of RANKL in the bone niche. Osteoprotegerin
(OPG) is a decoy receptor of RANKL that inhibits RANK-RANKL binding and
inhibit osteoclastogenesis. Higher RANKL/OPG ratio triggers osteoclastogenesis
and osteoclast activity. Membrane-bound RANKL has higher osteoclastogenesis
potential via cell-to-cell contact with osteoclast precursor. It has been reported that
MLO-Y4 osteocytes produce enough amount of soluble RANKL to stimulate
osteoclastogenesis in vitro [114]. Although osteocytes are buried in bone matrix,
their extended cell projections could facilitate the direct contact with osteoclast
precursor. Therefore, both soluble and membrane-bound osteocytic RANKL could
have potential to modulate osteoclastogenesis [115]. In vitro osteocyte-unloading
upregulates RANKL/OPG ratio [116••]. Mechanical loading has been reported to
inhibit RANKL/OPG ratio in osteocytes, and thereby inhibit osteoclast formation
and activity [117]. Moreover, mechanical loading inhibits inflammation-induced
osteocyte-to-osteoclast communication via downregulation of RANKL/OPG ratio
[5]. This indicates a key role of osteocyte mechanotransduction in bone
homeostasis by regulating RANKL/OPG-mediated osteoclastogenesis.
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IGF1 Signaling
Insulin-like growth factor 1 (IGF1) is mainly produced in liver and also in various
non-hepatic tissues, including muscle and bone. IGF1 plays a role in cell survival,
growth, differentiation, and cell cycle progression. In circulation, IGF binding
proteins bind to IGF1 and determine the bioavailability of IGF1 to interact with its
receptor IGF1-R. IGF1 is a promising anti-atrophy agent and induces skeletal
myotube hypertrophy [118]. IGF1 deficiency in mice decreases bone mineral
density and bone size [119, 120]. Complete deletion of IGF1 in mice alters both
direct and indirect interaction between osteoblastic cells and osteoclast precursor
cells by reducing RANKL and MCSF production and inhibits osteoclastogenesis
and thereby causes high BV/TV [121]. IGF1 signaling pathway plays an important
role in bone cell mechanotransduction. Mechanically loading of rat tibia increases
IGF1 expression in osteocytes [55, 122]. IGF1 deletion in osteocytes abolishes the
osteogenic response to mechanical loading [123]. IGF1 mediates PTH/PTHrP
signaling in osteocytes and regulates periosteal bone formation and intracortical
remodeling [124, 125]. Conditional disruption of IGF1 in osteocytes abolishes
mechanical loading-induced early upregulation of Cox2, c-Fos, and Wnt10b
expression. Similarly, mechanical loading fails to reduce Sost expression of IGF1-
deficient osteocytes [123]. IGF1 overexpression in osteoblasts enhances
mechanical loading responsiveness in mice bone, and this effect was reversed by
osteoblastic conditional IGF1 disruption [126, 127]. IGF1R is essential for
mechanical loading-induced periosteal bone formation [128]. Mechanical loading-
mediated anabolic effect on periosteal bone mass is local IGF1 release dependent
[127]. Mature osteoblast conditional knockout of IGF1R inhibits the mechanical
loading-induced periosteal bone formation [129]. Similarly, BMSCs from unloaded
mice bone fail to respond to IGF1 treatment in vitro by inhibiting the activation of
IGF1 signaling despite unchanged IGF1R level and normal binding of IGF1 to
IGF1R. However, the molecular mechanism of osteocyte mechanoresponse-
mediated effect on IGF1/IGF1R signaling in BMSCs is still unclear. All the
findings from literature strongly corroborate the key role of IGF1/IGF1R signaling
in osteoblast/osteocyte mechanotransduction.
BMP2 Signaling Pathway
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Bone morphogenetic proteins (BMPs) are major and indispensable players during
bone regeneration and bone homeostasis. Among 26 BMPs, BMP2, -4, -6, -7, and
-9 play roles in bone morphogenesis [130]. It has been reported that mechanical
loading upregulates BMP7 but not BMP2 in vitro, and this effect on BMP7
upregulation was likely via vitamin D receptor [76]. Wang and colleagues reported
that mechanical loading induces BMP7 in osteocytes and rescues glucocorticoid-
induced osteocyte apoptosis via activation of PI3K/AKT/GSK3β signaling [131].
BMP2 stimulation and mechanical loading synergistically regulate immediate early
BMP-induced signaling events [132]. Mechanical loading modulates the
stimulatory effect of exogenous BMP2 treatment in a rat nonunion fracture model
[133]. Similarly, mutual interaction between mechanical loading and BMP2
signaling during osteogenic differentiation of BMSCs has been reported.
Moreover, BMP type I and type II receptors co-localize with αvβ integrins. The
αvβ integrins are essential for BMP2-mediated osteoblast differentiation [134].
Similarly, αvβ integrins are the key components of focal adhesion and work as
mechanoreceptor in osteocytes; this supports the mutual interaction between
BMP2 signaling and osteocyte mechanotransduction.
Other Signaling Pathways
Dickkopf-related protein 1 (DKK1), a negative regulator of Wnt signaling, is
mainly expressed by osteocytes. Mechanical loading inhibits DKK1 expression in
osteocytes that facilitate upregulation of Wnt signaling [135]. Interleukin-6 (IL-6),
a proinflammatory cytokine, presents in elevated level in the early stage of fracture
healing. The elevated level of IL-6 in the early stage of fracture healing is
supposed to trigger the bone healing process. IL-6 is a highly mechanosensitive
gene, which rapidly upregulates in response to mechanical stimulation in both
osteoblasts and osteocytes [5, 9, 136–138]. Mechanical loading of bone cells gives
a parallel increase of IL-6 and PGE [137]. Inhibition of IL-6 reduces mechanical
loading-induced PGE2 and vice versa [137]. Similarly, hind limb unloading rat
model shows a lower level of IL-6 [139]. IL-6 enhances osteoclastogenesis, but its
role in osteoblast differentiation is still a controversy [137, 138, 140]. Similarly,
the exact role of mechanical loading-induced IL-6 in bone homeostasis has to be
further investigated. Vascular endothelial growth factor (VEGF) is a growth factor
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produced by a variety of cells, including endothelial cell and osteoblast lineage
cells. Osteoblast lineage cell-produced VEGF plays a vital role in osteogenesis-
angiogenesis coupling and facilitates bone defect healing [141]. Mechanical
stimuli have been reported to enhance osteocytic-VEGF production [142]. Cyclic
loading of osteoblast-loaded bone-like construct enhances VEGF expression,
indicating the possible use of mechanical loading in bone tissue engineering [143].
Similarly, VEGF receptor 2 activation is essential for the mechanical stimuli-
mediated promotion of osteocyte survival [144].
AQ2
MiRNAs are involved in bone cell proliferation, differentiation, and regulation of
bone remodeling. Recent reports from literature indicate an important role of
miRNAs in mechanical loading-mediated bone homeostasis [145]. Mechanical
loading has been reported to upregulate miR4943p, miR146a5p, miR2103p, and
miR12473p expression in MC3T3 osteoblasts. Mechanical loading inhibits
osteoblast proliferation via upregulation of miR4943p [146]. Zuo and colleagues
reported that mechanical loading upregulates Runx2 expression in osteoblasts via
inhibition of miR103a [147••]. Mechanically stimulated osteocytes promote
osteoblast differentiation via miR29b3p [148]. Extracellular vesicles, including
exosomes, are the carrier of miRNAs from one cell to other cells. Extracellular
vesicles from mechanically stimulated osteocytes have been reported to promote
bone formation [45]. Extracellular vesicles from mechanically stimulated
osteocytes-mediated bone formation might be via miRNAs; therefore, profiling of
miRNAs in these extracellular vesicles is essential to unravel the miRNAs
involved and underlying mechanism of bone formation.
Factors Affecting Osteocyte Mechanotransduction
Aging is one of the factors affecting osteocyte mechanotransduction. Mechanical
loading fails to rescue aging-related bone mass in old mice. Mechanical loading-
mediated upregulation of Wnt signaling and downregulation of sclerostin and
DKK1 is disrupted in old mice [135]. Exercise reduces the sclerostin level in
young boys but upregulates in adult men [109]. In a recent review, Hemmatian and
colleagues point out that declined number of osteocytes, morphological alteration
of osteocyte lacuna canalicular networks, and change in osteocyte shape (smaller
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and spherical) are main factors affecting osteocyte mechanotransduction in aged
people [149]. Similarly, declined level of estrogen and its receptors in aged female
might affect osteocyte mechanotransduction. Estrogen-estrogen receptor (ER)
signaling plays an important role in osteocyte survival and osteocyte
mechanotransduction as discussed in a review by Sapir-Koren et al. [150].
Mechanotransduction-mediated osteocyte anti-apoptotic effect is regulated by
membrane-localized ERα and/or ERβ [151]. The expression level of ERα and ERβ
in osteocytes is mainly regulated by estrogen. ERα is essential for osteocyte
mechanotransduction. Absence of ERα or ERβ in mice diminishes the osteocyte
response to mechanical loading [152]. Postmenopausal estrogen deficiency might
reduce expression of ERs in osteocytes disrupting the osteocyte
mechanotransduction. Tamoxifen, an estrogen agonist, modulates estrogen’s role in
activating osteocyte ER-mediated post-loading mechanisms [153]. Therefore,
appropriate modulators of ER activity, such as tamoxifen, could be therapeutic
drugs to enhance loading-related bone regeneration in estrogen-deficient females.
Similarly, osteoporosis has been reported to affect osteocyte mechanosensitivity.
Altered cortical and trabecular bone architecture and bone marrow contents in
osteoporosis could be the factors affecting the loading pattern in the bone. Bone
cells from osteoporotic patients showed an abnormal response to mechanical
loading [154]. As mentioned above, the declined level of estrogen and ERs in
osteoporosis could also affect osteocyte mechanosensitivity. Moreover, systemic
inflammatory conditions upregulate osteocytic sclerostin production [9].
Inflammatory cytokines have an adverse effect on osteocyte mechanotransduction.
Inflammatory cytokines are elevated systematically or in bone niche during
systemic inflammatory diseases such as rheumatoid arthritis, COPD, chronic
kidney disease as well as during cancer and cancer metastasis to bone. Increased
level of sclerostin in bone is observed during inflammatory conditions such as
periodontitis [155, 156] and cancer metastasis in bone [157]. The elevated level of
sclerostin inhibits bone’s adaptive response to mechanical loading [102, 158].
Physical exercise alleviates osteoporosis in chronic kidney disease rat model via
decreasing sclerostin production [159]. Sclerostin antibody treatment and
mechanical loading have shown a synergistic anabolic effect on bone regeneration
[160]. Kogawa and colleagues reported that sclerostin inhibits osteocyte-mediated
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contribution to bone mineral accretion and mechanical properties of bone by
modulating the dimensions of the lacuno-canalicular porosity and the composition
of the periosteocyte matrix [102]. Therefore, a combination of anti-sclerostin
treatment and mechanical loading could be a better approach to enhance bone
regeneration in inflammatory conditions.
Recently Stegen and colleagues reported that deletion of oxygen sensor prolyl
hydroxylase (PHD) 2 in osteocytes rescues the estrogen deficiency or mechanical
unloading-induced bone loss, via upregulation of Wnt/β-catenin signaling and
downregulation of sclerostin expression. Moreover, deletion of PHD2 robustly
enhances HIF-1α production in osteocytes [161]. However, the exact role of HIF-
1α in loading-induced bone formation is still controversial. Riddle and colleagues
reported that HIF-1α negatively regulates mechanical loading-mediated bone
formation [162]. Various therapeutic treatments have shown an inhibitory effect on
osteocyte mechanosensitivity. Glucocorticoid treatment induces bone loss via a
direct effect on bone cell function, including osteoblasts and osteocytes. High-dose
prednisolone treatment strongly inhibits the mechanical loading-induced increase
in trabecular BMD and abolishes the loading-induced increase in cortical bone
mass [163]. High dose of prednisolone abolished loading-induced osteocyte
number and viability, possibly via inhibition of osteoblast differentiation and
function [163]. A clinically relevant dose of vitamin A inhibits mechanical
loading-induced anabolic effect on bone formation, mainly via suppressing
osteoblast activity [164]. Type 1 diabetes affects osteocyte survival and function,
including mechanoresponse. Impaired bone’s responses to mechanical loading
have been impaired in type I diabetes [165]. High glucose inhibits osteocyte
mechanosignaling responses and attenuates the anti-apoptotic effect of loading
[166].
Osteocyte Mechanotransduction in Bone and Non-Bone-Related Clinical
Complications
Systemic inflammation has a direct correlation with bone loss. During systemic
inflammation, various inflammatory cytokine levels are elevated in blood
circulation and bone niche. Among them, IL1β, TNFα, IL6, and MMPs are major
proinflammatory cytokines affecting bone cell function and bone homeostasis. It
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has been reported that erogenous IL6 does not alter osteocyte mechanosensitivity,
but IL6 produced by osteocyte in response to mechanical loading affects bone cell
function [136]. IL1β and TNFα induce osteocyte apoptosis [88, 167]. Interestingly,
mechanical loading of osteocytes inhibits TNFα-induced osteocyte apoptosis
[167]. Moreover, IL1β and TNFα inhibits osteocyte mechanosensitivity and
reduces mechanical loading-induced osteocytic NO release via abrogation
intracellular calcium ion concentration [88]. IL1β induces osteocyte-mediated
osteoclastogenesis, and mechanical loading of osteocytes reverses this effect [168].
Mechanical loading of osteocytes inhibits IL17-induced osteoclastogenesis [169].
Membrane type matrix metalloproteinase-1 (MT1-MMP) is expressed in
osteocytes affect bone homeostasis. Mechanical loading inhibits MT1-MMP
expression in MLO-Y4 osteocytes. MT1-MMP knockdown increases the number
and size of focal adhesion in osteocytes and enhances the osteocyte response to
mechanical loading [72]. We have reported that a cocktail of proinflammatory
cytokines present in rheumatoid arthritic patient’s serum (RA-serum) affect bone
cell function and amplifies inflammation in a bone niche via inducing multiple
cytokine production by osteoblasts and osteocytes [5, 170, 171••]. We have also
reported that RA-serum enhances osteocyte to osteoclast communication, and
mechanical loading reverses this effect [5]. Inflammatory cytokines have a
catabolic effect either on osteocyte mechanosensitivity or osteocyte function and
osteocyte-communications to other bone cells. Mechanical loading of osteocytes
seems to reverse the adverse effect of inflammation on osteocyte function and
osteocyte-communication to other bone cells.
Mechanical loading of osteocytes by physical exercise has been reported to
increase serum estradiol in ovariectomized rats as well as increase serum
testosterone level in elderly man, and this increase of hormone levels directly
correlates with the increase of bone mass and strength. Implant failure due to poor
implant osseointegration is frequently observed in dental and orthopedic clinics. Li
and colleagues have recently reported that mechanical loading of peri-implant-
bone after implant insertion enhanced implant fixation and osseointegration in
estrogen-deficient mice model [172]. This indicates the mechanical stimulation as
a new therapeutic approach to prevent implant failure. During cancer bone
metastasis, the tumor cells affect neighboring osteocytes. Mechanical loading of
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bone protects cancer bone metastasis, but the exact mechanism is still unknown
[173••, 174]. Recently, Wang and colleagues reported that mechanically loaded
breast cancer cells alter osteocyte mechanosensitivity by enhancing osteocyte
dendrite formation [175].
Muscle and bone communicate with each other via mechanical and biochemical
signaling [176, 177]. Such communication plays a crucial role to maintain muscle
and bone mass. Skeletal muscle-secreted factors have been reported to prevent
glucocorticoid-induced osteocyte apoptosis via activation of Wnt/β-catenin
signaling [178]. The exercise-induced muscle factor β-aminoisobutyric acid
prevents osteocyte cell death induced by reactive oxygen species [179].
Mechanical loading exerts anabolic effect not only to the bone but also to muscle.
Mechanically loaded osteocytes promote myogenesis, but the mechanically loaded
osteoblasts fail to do so. Osteocytic Wnt-3a upregulation regulates the
mechanically stimulated osteocytes-mediated myogenic effect [180]. This indicates
a critical role of osteocytes in unloading-induced muscle and bone loss.
Various cancers, including breast and lung, have a high rate of bone metastasis.
Bone cells-cancer cells communication plays a vital role in cancer bone metastasis
and metastasis-related clinical complication. The osteocyte is the main source of
RANKL and sclerostin; both the molecules have a pivotal role in bone remodeling
and cancer-related osteolysis. Mechanically stimulated osteocytes not only
promote bone formation but also reduce the breast cancer metastasis to bone.
Mechanical loading on osteocytes has been reported to inhibit breast cancer cell
migration and adhesion. Mechanically loaded osteocytes enhance cancer cell
apoptosis via signaling through osteoclasts and endothelial cells [181, 182••].
Fluid flow-mediated osteocyte mechanostimulation reduces breast cancer
extravasation [183]. Similarly, Lynch and colleagues had reported that in vivo
tibial loading inhibits tumor formation in bone niche and tumor-associated
osteolysis in a human metastatic breast cancer model [174]. Multiple myeloma is
the second most prevalent hematologic malignancy that causes aggressive
osteocytic lesions [184, 185]. Pagnotti et al. reported that the mechanical stimuli in
the form of low-intensity vibration alleviates the multiple myeloma progression
and protects the myeloma-induced osteolysis and reduction in bone quality [173].
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This indicates the protective role of mechanical stimuli against the cancer-induced
bone loss.
Conclusions
Osteocytes have the ability to translate mechanical stimuli to bone anabolic
cellular signaling, and various cellular mechanisms such as Ca oscillation,
primary cilia deflection, and focal adhesion are involved in this process. In
response to mechanical stimuli, osteocytes release NO, PGE , and ATPs and
regulate multiple cellular signaling such as Wnt/β-catenin, RANKL/OPG, BMP,
PTH, IGF1, and others. These signaling pathways are involved in physiology and
pathology of bone and other vital organs as indicated in Fig. 1. Therefore, the
mechanical loading of bone could be the therapeutic approach to treat bone and
non-bone-related clinical complications. The future research focusing on the
development of the cost-effective, patient-friendly, and non-invasive mechanical
loading strategies are essential for clinical application of osteocyte
mechanotransduction. Low-intensity exercise regimes, frequency, and intensity
optimized vibration platform, and low-intensity pulsed ultrasound could help
osteoporotic patient or astronauts to maintain bone mass or alleviate other diseases
such as cancer metastasis to bone. Osteocyte-derived extracellular vesicles,
including exosomes, play a crucial role in bone regeneration and cancer metastasis
to bone. Similarly, osteocyte and osteoblast primary cilia have a robust potential to
translate mechanical stimuli to cellular signaling. Modulation of primary
ciliogenesis in osteoblasts and osteocytes could be the future research direction to
treat various bone and non-bone diseases. Extracellular vesicles carry various
proteins, cell signaling molecules, miRNA, and piRNA produced by cells and
transfer to the surrounding cells. Future research focusing on the molecular
mechanism of mechanically loaded osteocyte-released extracellular vesicles
involved in bone regeneration could reveal novel therapeutic targets to treat bone
and non-bone-related clinical complications. Among the total RNA expressed in
cells, the coding RNA (mRNA) contains only 3%, and the remaining 97% are non-
coding RNAs such as miRNAs, circular RNAs, lncRNAs, shRNAs, and piRNAs.
Recent advances in technologies such as RNA sequencing, functional analysis
tools, and bioinformatics tools had revealed the role of non-coding RNAs in
2+
2
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various cellular signaling and biological activities, including development and
diseases [186–190]. Expression pattern of non-coding RNAs during mechanical
loading of osteocytes and their role in osteocyte mechanotransduction have not
been investigated yet. Therefore, future studies focusing on the role of non-coding
RNAs in osteocyte functions are urgently needed. Angiogenesis and osteogenesis-
angiogenesis coupling play vital role in bone regeneration and bone homeostasis
[191]. However, the effect of osteocyte mechanotransduction on angiogenesis has
not been explored yet. Similarly, osteo-immunomodulation is another vital aspect
of skeletal biology [192]. The role of osteocyte mechanosensitivity in immune cell
differentiation and function such as macrophage polarization, T regulatory cell
formation and function, B cell function, NK cell maturation and function, and vice
versa is another important future research aspect. Future research focusing on
approaches to enhance osteocyte mechanosensitivity and to unveil the novel
signaling pathways and target might be potential strategy to treat various bone and
non-bone clinical problems via osteocyte mechanotransduction.
Fig. 1
Schematic diagram illustrates the mechanism of osteocyte-mediated translation of
mechanical stimuli to cellular signaling
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published
maps and institutional affiliations.
Funding Information
This work was supported by Project of Education of Guangdong Province, China
(2017KQNCX162), Project of Guangzhou Municipal Health Commission, China
(20181A011103), and the Project of Liwan District Science and Technology,
Gunagzhou, China (201804015).
Compliance with Ethical Standards
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Conflict of Interest Yongyong Yan, Liping Wang, Linhu Ge, Janak L. Pathak
declare no conflict of interest.
Human and Animal Rights and Informed Consent All reported
studies/experiments with human or animal subjects performed by the authors have
been previously published and complied with all applicable ethical standards
(including the Helsinki Declaration and its amendments, institutional/national
research committee standards, and international/national/institutional guidelines).
References
Papers of particular interest, published recently, have been highlighted as: •
Of importance •• Of major importance
1. Cowin SC. On mechanosensation in bone under microgravity. Bone.
1998;22(5 Suppl):119S–25S.
2. Zerwekh JE, Ruml LA, Gottschalk F, Pak CY. The effects of twelve weeks
of bed rest on bone histology, biochemical markers of bone turnover, and
calcium homeostasis in eleven normal subjects. J Bone Miner Res.
1998;13(10):1594–601.
3. Vico L, Hargens A. Skeletal changes during and after spaceflight. Nat Rev
Rheumatol. 2018;14(4):229–45.
4. •• Grimm D, Grosse J, Wehland M, Mann V, Reseland JE, Sundaresan A, et
al. The impact of microgravity on bone in humans. Bone. 2016;87:44–56.
Reviewed the effect of micro-gravity on bone loss in human and
experimental animals. Space flight-induced bone loss can be rescued in
some extent by physical exercise and other interventions such as diet and
medications.
5. Pathak JL, Bravenboer N, Luyten FP, Verschueren P, Lems WF, Klein-
Nulend J, et al. Mechanical loading reduces inflammation-induced human
1/16/20, 2:56 PMe.Proofing
Page 22 of 45https://eproofing.springer.com/journals_v2/printpage.php?token=t6UJMSWWIEq7xkPi7P6HHghsaQhfr0zzytCvR1mmCKY
osteocyte-to-osteoclast communication. Calcif Tissue Int. 2015;97(2):169–78.
6. Fahlgren A, Bratengeier C, Semeins CM, Klein-Nulend J, Bakker AD.
Supraphysiological loading induces osteocyte-mediated osteoclastogenesis in a
novel in vitro model for bone implant loosening. J Orthop Res.
2018;36(5):1425–34.
7. Delgado-Calle J, Bellido T. Osteocytes and skeletal pathophysiology. Curr
Mol Biol Rep. 2015;1(4):157–67.
8. Delgado-Calle J, Tu X, Pacheco-Costa R, McAndrews K, Edwards R,
Pellegrini GG, et al. Control of bone anabolism in response to mechanical
loading and PTH by distinct mechanisms downstream of the PTH receptor. J
Bone Miner Res. 2017;32(3):522–35.
9. • Zhou M, Li S, Pathak JL. Pro-inflammatory cytokines and osteocytes. Curr
Osteoporos Rep. 2019;17(3):97–104. Reviewed the role of inflammatory
cytokines in osteocytes survival and function. Inflammatory cytokines
upregulate osteocyte-derived expression of sclerostin, RANKL, TNFα,
FGF23, DKK1, and other signaling molecules thereby cause bone and non-
bone related complications.
10. Wang P, Tang C, Wu J, Yang Y, Yan Z, Liu X, et al. Pulsed electromagnetic
fields regulate osteocyte apoptosis, RANKL/OPG expression, and its control of
osteoclastogenesis depending on the presence of primary cilia. J Cell Physiol.
2019;234(7):10588–601.
11. O'Brien CA, Nakashima T, Takayanagi H. Osteocyte control of
osteoclastogenesis. Bone. 2013;54(2):258–63.
12. Tu X, Delgado-Calle J, Condon KW, Maycas M, Zhang H, Carlesso N, et
al. Osteocytes mediate the anabolic actions of canonical Wnt/beta-catenin
signaling in bone. Proc Natl Acad Sci U S A. 2015;112(5):E478–86.
1/16/20, 2:56 PMe.Proofing
Page 23 of 45https://eproofing.springer.com/journals_v2/printpage.php?token=t6UJMSWWIEq7xkPi7P6HHghsaQhfr0zzytCvR1mmCKY
13. Tu X, Rhee Y, Condon KW, Bivi N, Allen MR, Dwyer D, et al. Sost
downregulation and local Wnt signaling are required for the osteogenic
response to mechanical loading. Bone. 2012;50(1):209–17.
14. van Bezooijen RL, ten Dijke P, Papapoulos SE, Lowik CW.
SOST/sclerostin, an osteocyte-derived negative regulator of bone formation.
Cytokine Growth Factor Rev. 2005;16(3):319–27.
15. Hamersma H, Gardner J, Beighton P. The natural history of sclerosteosis.
Clin Genet. 2003;63(3):192–7.
16. Van Buchem FS, Hadders HN, Ubbens R. An uncommon familial systemic
disease of the skeleton: hyperostosis corticalis generalisata familiaris. Acta
Radiol. 1955;44(2):109–20.
17. Van Hul W, Balemans W, Van Hul E, Dikkers FG, Obee H, Stokroos RJ, et
al. Van Buchem disease (hyperostosis corticalis generalisata) maps to
chromosome 17q12-q21. Am J Hum Genet. 1998;62(2):391–9.
18. Bonewald LF. The amazing osteocyte. J Bone Miner Res. 2011;26(2):229–
38.
19. Fujii O, Tatsumi S, Ogata M, Arakaki T, Sakaguchi H, Nomura K, et al.
Effect of osteocyte-ablation on inorganic phosphate metabolism: analysis of
bone-kidney-gut axis. Front Endocrinol (Lausanne). 2017;8:359.
20. Tresguerres FGF, Torres J, Lopez-Quiles J, Hernandez G, Vega JA,
Tresguerres IF. The osteocyte: a multifunctional cell within the bone. Ann Anat.
2020;227:151422.
21. Quarles LD. FGF23, PHEX, and MEPE regulation of phosphate
homeostasis and skeletal mineralization. Am J Physiol Endocrinol Metab.
2003;285(1):E1–9.
1/16/20, 2:56 PMe.Proofing
Page 24 of 45https://eproofing.springer.com/journals_v2/printpage.php?token=t6UJMSWWIEq7xkPi7P6HHghsaQhfr0zzytCvR1mmCKY
22. Dussold C, Gerber C, White S, Wang X, Qi L, Francis C, et al. DMP1
prevents osteocyte alterations, FGF23 elevation and left ventricular
hypertrophy in mice with chronic kidney disease. Bone Res. 2019;7:12.
23. Martin A. Bone and heart health in chronic kidney disease: role of dentin
matrix protein 1. Curr Opin Nephrol Hypertens. 2019;28(4):297–303.
24. Zhang BB, Hou RT, Zou Z, Luo TT, Zhang Y, Wang LY, et al.
Mechanically induced autophagy is associated with ATP metabolism and
cellular viability in osteocytes in vitro. Redox Biol. 2018;14:492–8.
25. •• Thi MM, Suadicani SO, Schaffler MB, Weinbaum S, Spray DC.
Mechanosensory responses of osteocytes to physiological forces occur along
processes and not cell body and require alphaVbeta3 integrin. Proc Natl Acad
Sci U S A. 2013;110(52):21012–7. Demonstrated osteocyte cell processes but
not the cell bodies are mechanoresponsive. The αVβ3 integrin plays a key
role in osteocyte-polarized mechanosensing and mechanotransduction.
26. Martin RB. Toward a unifying theory of bone remodeling. Bone.
2000;26(1):1–6.
27. Tatsumi S, Ishii K, Amizuka N, Li M, Kobayashi T, Kohno K, et al.
Targeted ablation of osteocytes induces osteoporosis with defective
mechanotransduction. Cell Metab. 2007;5(6):464–75.
28. Zhang D, Zhou C, Wang Q, Cai L, Du W, Li X, et al. Extracellular matrix
elasticity regulates osteocyte gap junction elongation: involvement of paxillin
in intracellular signal transduction. Cell Physiol Biochem. 2018;51(3):1013–26.
29. Klein-Nulend J, van der Plas A, Semeins CM, Ajubi NE, Frangos JA,
Nijweide PJ, et al. Sensitivity of osteocytes to biomechanical stress in vitro.
FASEB J. 1995;9(5):441–5.
30. Malone AM, Anderson CT, Tummala P, Kwon RY, Johnston TR, Stearns T,
1/16/20, 2:56 PMe.Proofing
Page 25 of 45https://eproofing.springer.com/journals_v2/printpage.php?token=t6UJMSWWIEq7xkPi7P6HHghsaQhfr0zzytCvR1mmCKY
et al. Primary cilia mediate mechanosensing in bone cells by a calcium-
independent mechanism. Proc Natl Acad Sci U S A. 2007;104(33):13325–30.
31. Ponik SM, Triplett JW, Pavalko FM. Osteoblasts and osteocytes respond
differently to oscillatory and unidirectional fluid flow profiles. J Cell Biochem.
2007;100(3):794–807.
32. Hung CT, Pollack SR, Reilly TM, Brighton CT. Real-time calcium
response of cultured bone cells to fluid flow. Clin Orthop Relat Res.
1995;313:256–69.
33. Reich KM, Frangos JA. Effect of flow on prostaglandin E2 and inositol
trisphosphate levels in osteoblasts. Am J Phys. 1991;261(3 Pt 1):C428–32.
34. Lu XL, Huo B, Park M, Guo XE. Calcium response in osteocytic networks
under steady and oscillatory fluid flow. Bone. 2012;51(3):466–73.
35. Jing D, Baik AD, Lu XL, Zhou B, Lai XH, Wang LY, et al. In situ
intracellular calcium oscillations in osteocytes in intact mouse long bones under
dynamic mechanical loading. FASEB J. 2014;28(4):1582–92.
36. Hu M, Tian GW, Gibbons DE, Jiao J, Qin YX. Dynamic fluid flow induced
mechanobiological modulation of in situ osteocyte calcium oscillations. Arch
Biochem Biophys. 2015;579:55–61.
37. Adachi T, Aonuma Y, Ito S, Tanaka M, Hojo M, Takano-Yamamoto T, et al.
Osteocyte calcium signaling response to bone matrix deformation. J Biomech.
2009;42(15):2507–12.
38. •• Lewis KJ, Frikha-Benayed D, Louie J, Stephen S, Spray DC, Thi MM, et
al. Osteocyte calcium signals encode strain magnitude and loading frequency in
vivo. Proc Natl Acad Sci USA. 2017;114(44):11775–80. Reported a mouse
model with an osteocyte-targeted genetically encoded Ca indicator to
study Ca2+ signaling in osteocytes in their authentic in vivo environment.
2+
2+
1/16/20, 2:56 PMe.Proofing
Page 26 of 45https://eproofing.springer.com/journals_v2/printpage.php?token=t6UJMSWWIEq7xkPi7P6HHghsaQhfr0zzytCvR1mmCKY
Ca signaling of osteocytes in vivo, both individually and as networks,
responds to mechanical loading.
39. Lu XL, Huo B, Chiang V, Guo XE. Osteocytic network is more responsive
in calcium signaling than osteoblastic network under fluid flow. J Bone Miner
Res. 2012;27(3):563–74.
40. Hung CT, Allen FD, Pollack SR, Brighton CT. Intracellular Ca2+ stores
and extracellular Ca2+ are required in the real-time Ca2+ response of bone
cells experiencing fluid flow. J Biomech. 1996;29(11):1411–7.
41. Chen X, Guo J, Yuan Y, Sun Z, Chen B, Tong X, et al. Cyclic compression
stimulates osteoblast differentiation via activation of the Wnt/beta-catenin
signaling pathway. Mol Med Rep. 2017;15(5):2890–6.
42. Miyauchi A, Gotoh M, Kamioka H, Notoya K, Sekiya H, Takagi Y, et al.
AlphaVbeta3 integrin ligands enhance volume-sensitive calcium influx in
mechanically stretched osteocytes. J Bone Miner Metab. 2006;24(6):498–504.
43. Cabahug-Zuckerman P, Stout RF Jr, Majeska RJ, Thi MM, Spray DC,
Weinbaum S, et al. Potential role for a specialized beta3 integrin-based
structure on osteocyte processes in bone mechanosensation. J Orthop Res.
2018;36(2):642–52.
44. Brown GN, Leong PL, Guo XE. T-type voltage-sensitive calcium channels
mediate mechanically-induced intracellular calcium oscillations in osteocytes
by regulating endoplasmic reticulum calcium dynamics. Bone. 2016;88:56–63.
45. •• Morrell AE, Brown GN, Robinson ST, Sattler RL, Baik AD, Zhen G, et
al. Mechanically induced Ca(2+) oscillations in osteocytes release extracellular
vesicles and enhance bone formation. Bone Res. 2018;6:6. Revealed
mechanical stimulation of osteocyte-mediated activation of Ca2+-
dependent contraction enhances the production and release of EVs
containing bone regulatory proteins. Blocking Ca signaling significantly
2+
2+
1/16/20, 2:56 PMe.Proofing
Page 27 of 45https://eproofing.springer.com/journals_v2/printpage.php?token=t6UJMSWWIEq7xkPi7P6HHghsaQhfr0zzytCvR1mmCKY
attenuates adaptation to mechanical loading in vivo, suggesting a critical
role for Ca -mediated signaling in bone adaptation.
46. •• Burra S, Nicolella DP, Francis WL, Freitas CJ, Mueschke NJ, Poole K,
et al. Dendritic processes of osteocytes are mechanotransducers that induce the
opening of hemichannels. Proc Natl Acad Sci USA. 2010;107(31):13648–53.
Reported the importance of glycocalyx of the osteocyte dendritic process in
forming strong integrin attachments that probably serve as the
mechanotransducers and transmit the mechanical signals to the cell body
leading to the opening of hemichannels, which permits rapid exchange of
signaling factors required for bone remodeling.
47. Genetos DC, Kephart CJ, Zhang Y, Yellowley CE, Donahue HJ. Oscillating
fluid flow activation of gap junction hemichannels induces ATP release from
MLO-Y4 osteocytes. J Cell Physiol. 2007;212(1):207–14.
48. •• Bivi N, Pacheco-Costa R, Brun LR, Murphy TR, Farlow NR, Robling
AG, et al. Absence of Cx43 selectively from osteocytes enhances
responsiveness to mechanical force in mice. J Orthop Res. 2013;31(7):1075–81.
Illustrated the role of osteocytic Cx43 in mechanotransduction-mediated
anabolic response to the bone using osteocyte specific Cx43 knockout mice
model.
49. Cresswell EN, Nguyen TM, Horsfield MW, Alepuz AJ, Metzger TA,
Niebur GL, et al. Mechanically induced bone formation is not sensitive to local
osteocyte density in rat vertebral cancellous bone. J Orthop Res.
2018;36(2):672–81.
50. Zhang JN, Zhao Y, Liu C, Han ES, Yu X, Lidington D, et al. The role of the
sphingosine-1-phosphate signaling pathway in osteocyte mechanotransduction.
Bone. 2015;79:71–8.
51. Zaman G, Pitsillides AA, Rawlinson SC, Suswillo RF, Mosley JR, Cheng
MZ, et al. Mechanical strain stimulates nitric oxide production by rapid
2+
1/16/20, 2:56 PMe.Proofing
Page 28 of 45https://eproofing.springer.com/journals_v2/printpage.php?token=t6UJMSWWIEq7xkPi7P6HHghsaQhfr0zzytCvR1mmCKY
activation of endothelial nitric oxide synthase in osteocytes. J Bone Miner Res.
1999;14(7):1123–31.
52. Vatsa A, Smit TH, Klein-Nulend J. Extracellular NO signalling from a
mechanically stimulated osteocyte. J Biomech. 2007;40:S89–95.
53. Vatsa A, Mizuno D, Smit TH, Schmidt CF, MacKintosh FC, Klein-Nulend
J. Bio imaging of intracellular NO production in single bone cells after
mechanical stimulation. J Bone Miner Res. 2006;21(11):1722–8.
54. Ajubi NE, Klein-Nulend J, Alblas MJ, Burger EH, Nijweide PJ. Signal
transduction pathways involved in fluid flow-induced PGE2 production by
cultured osteocytes. Am J Phys. 1999;276(1):E171–8.
55. Lean JM, Jagger CJ, Chambers TJ, Chow JW. Increased insulin-like growth
factor I mRNA expression in rat osteocytes in response to mechanical
stimulation. Am J Phys. 1995;268(2 Pt 1):E318–27.
56. Kamel MA, Picconi JL, Lara-Castillo N, Johnson ML. Activation of beta-
catenin signaling in MLO-Y4 osteocytic cells versus 2T3 osteoblastic cells by
fluid flow shear stress and PGE2: implications for the study of
mechanosensation in bone. Bone. 2010;47(5):872–81.
57. Satir P, Christensen ST. Overview of structure and function of mammalian
cilia. Annu Rev Physiol. 2007;69:377–400.
58. Hua K, Ferland RJ. Primary cilia proteins: ciliary and extraciliary sites and
functions. Cell Mol Life Sci. 2018;75(9):1521–40.
59. Berbari NF, O'Connor AK, Haycraft CJ, Yoder BK. The primary cilium as
a complex signaling center. Curr Biol. 2009;19(13):R526–R35.
60. Yuan X, Serra RA, Yang SY. Function and regulation of primary cilia and
intraflagellar transport proteins in the skeleton. Ann N Y Acad Sci.
1/16/20, 2:56 PMe.Proofing
Page 29 of 45https://eproofing.springer.com/journals_v2/printpage.php?token=t6UJMSWWIEq7xkPi7P6HHghsaQhfr0zzytCvR1mmCKY
2015;1335:78–99.
61. •• Delling M, Indzhykulian AA, Liu X, Li Y, Xie T, Corey DP, et al.
Primary cilia are not calcium-responsive mechanosensors. Nature.
2016;531(7596):656–60. Kidney cells with calcium indicator encoded
primary cilia revealed that primary cilia-mediated mechanosensation is not
via cilia-specific Ca(2+) influxes.
62. Delaine-Smith RM, Sittichokechaiwut A, Reilly GC. Primary cilia respond
to fluid shear stress and mediate flow-induced calcium deposition in
osteoblasts. FASEB J. 2014;28(1):430–9.
63. Xiao Z, Dallas M, Qiu N, Nicolella D, Cao L, Johnson M, et al.
Conditional deletion of Pkd1 in osteocytes disrupts skeletal mechanosensing in
mice. FASEB J. 2011;25(7):2418–32.
64. Xiao ZS, Zhang SQ, Cao L, Qiu N, David V, Quarles LD. Conditional
disruption of Pkd1 in osteoblasts results in osteopenia due to direct impairment
of bone formation. J Biol Chem. 2010;285(2):1177–87.
65. Chen JC, Hoey DA, Chua M, Bellon R, Jacobs CR. Mechanical signals
promote osteogenic fate through a primary cilia-mediated mechanism. FASEB
J. 2016;30(4):1504–11.
66. Qiu N, Xiao Z, Cao L, Buechel MM, David V, Roan E, et al. Disruption of
Kif3a in osteoblasts results in defective bone formation and osteopenia. J Cell
Sci. 2012;125(Pt 8):1945–57.
67. Temiyasathit S, Tang WJ, Leucht P, Anderson CT, Monica SD, Castillo
AB, et al. Mechanosensing by the primary cilium: deletion of Kif3A reduces
bone formation due to loading. PLoS One. 2012;7(3):e33368.
68. Chen CS, Tan J, Tien J. Mechanotransduction at cell-matrix and cell-cell
contacts. Annu Rev Biomed Eng. 2004;6:275–302.
1/16/20, 2:56 PMe.Proofing
Page 30 of 45https://eproofing.springer.com/journals_v2/printpage.php?token=t6UJMSWWIEq7xkPi7P6HHghsaQhfr0zzytCvR1mmCKY
69. Geiger B, Bershadsky A, Pankov R, Yamada KM. Transmembrane
crosstalk between the extracellular matrix--cytoskeleton crosstalk. Nat Rev Mol
Cell Biol. 2001;2(11):793–805.
70. Goldmann WH. Role of vinculin in cellular mechanotransduction. Cell Biol
Int. 2016;40(3):241–56.
71. Zaidel-Bar R, Cohen M, Addadi L, Geiger B. Hierarchical assembly of
cell-matrix adhesion complexes. Biochem Soc Trans. 2004;32(Pt3):416–20.
72. Kulkarni RN, Bakker AD, Gruber EV, Chae TD, Veldkamp JBB, Klein-
Nulend J, et al. MT1-MMP modulates the mechanosensitivity of osteocytes.
Biochem Biophys Res Commun. 2012;417(2):824–9.
73. Bell S, Terentjev EM. Focal adhesion kinase: the reversible molecular
mechanosensor. Biophys J. 2017;112(11):2439–50.
74. Santos A, Bakker AD, Zandieh-Doulabi B, de Blieck-Hogervorst JMA,
Klein-Nulend J. Early activation of the beta-catenin pathway in osteocytes is
mediated by nitric oxide, phosphatidyl inositol-3 kinase/Akt, and focal
adhesion kinase. Biochem Biophys Res Commun. 2010;391(1):364–9.
75. Young SRL, Gerard-O'Riley R, Kim JB, Pavalko FM. Focal adhesion
kinase is important for fluid shear stress-induced mechanotransduction in
osteoblasts. J Bone Miner Res. 2009;24:411–24.
76. Santos A, Bakker AD, Willems HM, Bravenboer N, Bronckers AL, Klein-
Nulend J. Mechanical loading stimulates BMP7, but not BMP2, production by
osteocytes. Calcif Tissue Int. 2011;89(4):318–26.
77. Sun Z, Lambacher A, Fassler R. Nascent adhesions: from fluctuations to a
hierarchical organization. Curr Biol. 2014;24(17):R801–3.
78. Kaneko K, Ito M, Naoe Y, Lacy-Hulbert A, Ikeda K. Integrin alphav in the
1/16/20, 2:56 PMe.Proofing
Page 31 of 45https://eproofing.springer.com/journals_v2/printpage.php?token=t6UJMSWWIEq7xkPi7P6HHghsaQhfr0zzytCvR1mmCKY
mechanical response of osteoblast lineage cells. Biochem Biophys Res
Commun. 2014;447(2):352–7.
79. Geoghegan IP, Hoey DA, McNamara LM. Integrins in osteocyte biology
and mechanotransduction. Curr Osteoporos Rep. 2019;17(4):195–206.
80. Geoghegan IP, Hoey DA, McNamara LM. Estrogen deficiency impairs
integrin alphavbeta3-mediated mechanosensation by osteocytes and alters
osteoclastogenic paracrine signalling. Sci Rep. 2019;9(1):4654.
81. McNamara LM, Majeska RJ, Weinbaum S, Friedrich V, Schaffler MB.
Attachment of osteocyte cell processes to the bone matrix. Anat Rec
(Hoboken). 2009;292(3):355–63.
82. Bidwell JP, Pavalko FM. Mechanosomes carry a loaded message. Sci
Signal. 2010;3(153):pe51.
83. •• Sato AY, Li T, Robling AG. FAK expression in osteocytes is dispensable
for bone accrual and for the anabolic response of cortical and cancellous bone
to mechanical loading in female mice. J Bone Miner Res. 2018;32. Avialable at
https://www.asbmr.org/education/AbstractDetail?aid=048482c3-d377-4a4a-
98a5-20c68712a5b3 . The first time illustrated that the osteocytic FAK
expression in depensible for mechanical loading-mediated anabolic effect
on bone in vivo using FAK and FAK mice. This finding is contrary to
previous reports form the in vitro studies.
84. Fox SW, Chambers TJ, Chow JW. Nitric oxide is an early mediator of the
increase in bone formation by mechanical stimulation. Am J Phys. 1996;270(6
Pt 1):E955–60.
85. Turner CH, Takano Y, Owan I, Murrell GA. Nitric oxide inhibitor L-
NAME suppresses mechanically induced bone formation in rats. Am J Phys.
1996;270(4 Pt 1):E634–9.
ΔOT f/f
1/16/20, 2:56 PMe.Proofing
Page 32 of 45https://eproofing.springer.com/journals_v2/printpage.php?token=t6UJMSWWIEq7xkPi7P6HHghsaQhfr0zzytCvR1mmCKY
86. •• Nakashima T, Hayashi M, Fukunaga T, Kurata K, Oh-Hora M, Feng JQ,
et al. Evidence for osteocyte regulation of bone homeostasis through RANKL
expression. Nat Med. 2011;17(10):1231–4. Reported severe osteopetrotic
phenotype in osteocyte-specific RANKL knockout mice, indicating
osteocytes as a major source of RANKL in bone remodeling in vivo.
87. Xiong J, Onal M, Jilka RL, Weinstein RS, Manolagas SC, O'Brien CA.
Matrix-embedded cells control osteoclast formation. Nat Med.
2011;17(10):1235–41.
88. Bakker AD, Silva VC, Krishnan R, Bacabac RG, Blaauboer ME, Lin YC,
et al. Tumor necrosis factor alpha and interleukin-1beta modulate calcium and
nitric oxide signaling in mechanically stimulated osteocytes. Arthritis Rheum.
2009;60(11):3336–45.
89. Delgado-Calle J, Riancho JA, Klein-Nulend J. Nitric oxide is involved in
the down-regulation of SOST expression induced by mechanical loading. Calcif
Tissue Int. 2014;94(4):414–22.
90. Smith WL, Garavito RM, DeWitt DL. Prostaglandin endoperoxide H
synthases (cyclooxygenases)-1 and -2. J Biol Chem. 1996;271(52):33157–60.
91. Bakker AD, Klein-Nulend J, Burger EH. Mechanotransduction in bone
cells proceeds via activation of COX-2, but not COX-1. Biochem Biophys Res
Commun. 2003;305(3):677–83.
92. Joldersma M, Burger EH, Semeins CM, Klein-Nulend J. Mechanical stress
induces COX-2 mRNA expression in bone cells from elderly women. J
Biomech. 2000;33(1):53–61.
93. Cherian PP, Siller-Jackson AJ, Gu S, Wang X, Bonewald LF, Sprague E, et
al. Mechanical strain opens connexin 43 hemichannels in osteocytes: a novel
mechanism for the release of prostaglandin. Mol Biol Cell. 2005;16(7):3100–6.
1/16/20, 2:56 PMe.Proofing
Page 33 of 45https://eproofing.springer.com/journals_v2/printpage.php?token=t6UJMSWWIEq7xkPi7P6HHghsaQhfr0zzytCvR1mmCKY
94. Gupta A, Chatree S, Buo AM, Moorer MC, Stains JP. Connexin43
enhances Wnt and PGE2-dependent activation of beta-catenin in osteoblasts.
Pflugers Arch. 2019;471(9):1235–43.
95. Kringelbach TM, Aslan D, Novak I, Ellegaard M, Syberg S, Andersen CK,
et al. Fine-tuned ATP signals are acute mediators in osteocyte
mechanotransduction. Cell Signal. 2015;27(12):2401–9.
96. •• Cui Y, Niziolek PJ, MacDonald BT, Zylstra CR, Alenina N, Robinson
DR, et al. Lrp5 functions in bone to regulate bone mass. Nat Med.
2011;17(6):684–91 Indicated the anabolic role of activated osteocytic LRP5
signaling in bone mass, suggesting it as a possible approach to treat
osteoporosis.
97. Bullock WA, Pavalko FM, Robling AG. Osteocytes and mechanical
loading: the Wnt connection. Orthod Craniofacial Res. 2019;22(Suppl 1):175–
9.
98. • Lara-Castillo N, Kim-Weroha NA, Kamel MA, Javaheri B, Ellies DL,
Krumlauf RE, et al. In vivo mechanical loading rapidly activates beta-catenin
signaling in osteocytes through a prostaglandin mediated mechanism. Bone.
2015;76:58–66. Reported the rapid activation of β-catenin in vitro and in
vivo in response to mechanical loading of osteocytes is via the early release
of prostaglandin.
99. Sawakami K, Robling AG, Ai M, Pitner ND, Liu D, Warden SJ, et al. The
Wnt co-receptor LRP5 is essential for skeletal mechanotransduction but not for
the anabolic bone response to parathyroid hormone treatment. J Biol Chem.
2006;281(33):23698–711.
100. Saxon LK, Jackson BF, Sugiyama T, Lanyon LE, Price JS. Analysis of
multiple bone responses to graded strains above functional levels, and to disuse,
in mice in vivo show that the human Lrp5 G171V high bone mass mutation
increases the osteogenic response to loading but that lack of Lrp5 activity
1/16/20, 2:56 PMe.Proofing
Page 34 of 45https://eproofing.springer.com/journals_v2/printpage.php?token=t6UJMSWWIEq7xkPi7P6HHghsaQhfr0zzytCvR1mmCKY
reduces it. Bone. 2011;49(2):184–93.
101. Zhao L, Shim JW, Dodge TR, Robling AG, Yokota H. Inactivation of
Lrp5 in osteocytes reduces young's modulus and responsiveness to the
mechanical loading. Bone. 2013;54(1):35–43.
102. Kogawa M, Khalid KA, Wijenayaka AR, Ormsby RT, Evdokiou A,
Anderson PH, et al. Recombinant sclerostin antagonizes effects of ex vivo
mechanical loading in trabecular bone and increases osteocyte lacunar size. Am
J Phys Cell Phys. 2018;314(1):C53–61.
103. Robling AG, Niziolek PJ, Baldridge LA, Condon KW, Allen MR, Alam I,
et al. Mechanical stimulation of bone in vivo reduces osteocyte expression of
Sost/sclerostin. J Biol Chem. 2008;283(9):5866–75.
104. Morse A, McDonald MM, Kelly NH, Melville KM, Schindeler A, Kramer
I, et al. Mechanical load increases in bone formation via a sclerostin-
independent pathway. J Bone Miner Res. 2014;29(11):2456–67.
105. Reid IR. Targeting sclerostin in postmenopausal osteoporosis: focus on
romosozumab and blosozumab. BioDrugs. 2017;31(4):289–97.
106. Saliba W, El-Haddad B. Secondary hyperparathyroidism: pathophysiology
and treatment. J Am Board Fam Med. 2009;22(5):574–81.
107. Ma YL, Cain RL, Halladay DL, Yang X, Zeng Q, Miles RR, et al.
Catabolic effects of continuous human PTH (1--38) in vivo is associated with
sustained stimulation of RANKL and inhibition of osteoprotegerin and gene-
associated bone formation. Endocrinology. 2001;142(9):4047–54.
108. Jilka RL. Molecular and cellular mechanisms of the anabolic effect of
intermittent PTH. Bone. 2007;40(6):1434–46.
109. Falk B, Haddad F, Klentrou P, Ward W, Kish K, Mezil Y, et al.
1/16/20, 2:56 PMe.Proofing
Page 35 of 45https://eproofing.springer.com/journals_v2/printpage.php?token=t6UJMSWWIEq7xkPi7P6HHghsaQhfr0zzytCvR1mmCKY
Differential sclerostin and parathyroid hormone response to exercise in boys
and men. Osteoporos Int. 2016;27(3):1245–9.
110. Gardinier JD, Al-Omaishi S, Morris MD, Kohn DH. PTH signaling
mediates perilacunar remodeling during exercise. Matrix Biol. 2016;52–
54:162–75.
111. Maycas M, McAndrews KA, Sato AY, Pellegrini GG, Brown DM, Allen
MR, et al. PTHrP-derived peptides restore bone mass and strength in diabetic
mice: additive effect of mechanical loading. J Bone Miner Res.
2017;32(3):486–97.
112. Camirand A, Goltzman D, Gupta A, Kaouass M, Panda D, Karaplis A.
The role of parathyroid hormone-related protein (PTHrP) in osteoblast response
to microgravity: mechanistic implications for osteoporosis development. PLoS
One. 2016;11(7):e0160034.
113. •• Maycas M, Ardura JA, de Castro LF, Bravo B, Gortazar AR, Esbrit P.
Role of the parathyroid hormone type 1 receptor (PTH1R) as a mechanosensor
in osteocyte survival. J Bone Miner Res. 2015;30(7):1231–44. Reported
PTH1R as an important component of mechanical signal transduction in
osteocytes. PTH1R activation by PTHrP-independent and PTHrP-
dependent mechanisms is a key event for the prosurvival action induced by
mechanical stimulation in osteocytes.
114. Kurata K, Heino TJ, Higaki H, Vaananen HK. Bone marrow cell
differentiation induced by mechanically damaged osteocytes in 3D gel-
embedded culture. J Bone Miner Res. 2006;21(4):616–25.
115. Xiong J, O'Brien CA. Osteocyte RANKL: new insights into the control of
bone remodeling. J Bone Miner Res. 2012;27(3):499–505.
116. • Spatz JM, Wein MN, Gooi JH, Qu YL, Garr JL, Liu S, et al. The Wnt
inhibitor sclerostin is up-regulated by mechanical unloading in osteocytes in
1/16/20, 2:56 PMe.Proofing
Page 36 of 45https://eproofing.springer.com/journals_v2/printpage.php?token=t6UJMSWWIEq7xkPi7P6HHghsaQhfr0zzytCvR1mmCKY
vitro. J Biol Chem. 2015;290(27):16744–58. Showed mechanical unloading of
osteocytes in vitro as a upregulator of SOST/sclerostin and RANKL/OPG
ratio. This result highly supports the findings from in vivo mechanical
unloading studies and suggest osteocyte targeted therapy as a potential
approach to treat osteoporosis and disuse-induced bone loss.
117. You L, Temiyasathit S, Lee P, Kim CH, Tummala P, Yao W, et al.
Osteocytes as mechanosensors in the inhibition of bone resorption due to
mechanical loading. Bone. 2008;42(1):172–9.
118. Rommel C, Bodine SC, Clarke BA, Rossman R, Nunez L, Stitt TN, et al.
Mediation of IGF-1-induced skeletal myotube hypertrophy by
PI(3)K/Akt/mTOR and PI(3)K/Akt/GSK3 pathways. Nat Cell Biol.
2001;3(11):1009–13.
119. Mohan S, Baylink DJ. Impaired skeletal growth in mice with
haploinsufficiency of IGF-I: genetic evidence that differences in IGF-I
expression could contribute to peak bone mineral density differences. J
Endocrinol. 2005;185(3):415–20.
120. Bikle D, Majumdar S, Laib A, Powell-Braxton L, Rosen C, Beamer W, et
al. The skeletal structure of insulin-like growth factor I-deficient mice. J Bone
Miner Res. 2001;16(12):2320–9.
121. Wang Y, Nishida S, Elalieh HZ, Long RK, Halloran BP, Bikle DD. Role
of IGF-I signaling in regulating osteoclastogenesis. J Bone Miner Res.
2006;21(9):1350–8.
122. Reijnders CM, Bravenboer N, Tromp AM, Blankenstein MA, Lips P.
Effect of mechanical loading on insulin-like growth factor-I gene expression in
rat tibia. J Endocrinol. 2007;192(1):131–40.
123. Lau KHW, Baylink DJ, Zhou XD, Rodriguez D, Bonewald LF, Li ZH, et
al. Osteocyte-derived insulin-like growth factor I is essential for determining
1/16/20, 2:56 PMe.Proofing
Page 37 of 45https://eproofing.springer.com/journals_v2/printpage.php?token=t6UJMSWWIEq7xkPi7P6HHghsaQhfr0zzytCvR1mmCKY
bone mechanosensitivity. Am J Phys Endocrinol Metab. 2013;305(2):E271–
E81.
124. Saini V, Marengi DA, Barry KJ, Fulzele KS, Heiden E, Liu X, et al.
Parathyroid hormone (PTH)/PTH-related peptide type 1 receptor (PPR)
signaling in osteocytes regulates anabolic and catabolic skeletal responses to
PTH. J Biol Chem. 2013;288(28):20122–34.
125. Rhee Y, Allen MR, Condon K, Lezcano V, Ronda AC, Galli C, et al. PTH
receptor signaling in osteocytes governs periosteal bone formation and
intracortical remodeling. J Bone Miner Res. 2011;26(5):1035–46.
126. Gross TS, Srinivasan S, Liu CC, Clemens TL, Bain SD. Noninvasive
loading of the murine tibia: an in vivo model for the study of
mechanotransduction. J Bone Miner Res. 2002;17(3):493–501.
127. Kesavan C, Wergedal JE, Lau KH, Mohan S. Conditional disruption of
IGF-I gene in type 1alpha collagen-expressing cells shows an essential role of
IGF-I in skeletal anabolic response to loading. Am J Physiol Endocrinol Metab.
2011;301(6):E1191–7.
128. Sakata T, Wang Y, Halloran BP, Elalieh HZ, Cao J, Bikle DD. Skeletal
unloading induces resistance to insulin-like growth factor-I (IGF-I) by
inhibiting activation of the IGF-I signaling pathways. J Bone Miner Res.
2004;19(3):436–46.
129. Kubota T, Elalieh HZ, Saless N, Fong C, Wang YM, Babey M, et al.
Insulin-like growth factor-1 receptor in mature osteoblasts is required for
periosteal bone formation induced by reloading. Acta Astronaut.
2013;92(1):73–8.
130. Bessa PC, Casal M, Reis RL. Bone morphogenetic proteins in tissue
engineering: the road from the laboratory to the clinic, part I (basic concepts). J
Tissue Eng Regen Med. 2008;2(1):1–13.
1/16/20, 2:56 PMe.Proofing
Page 38 of 45https://eproofing.springer.com/journals_v2/printpage.php?token=t6UJMSWWIEq7xkPi7P6HHghsaQhfr0zzytCvR1mmCKY
131. Wang Z, Guo J. Mechanical induction of BMP-7 in osteocyte blocks
glucocorticoid-induced apoptosis through PI3K/AKT/GSK3beta pathway. Cell
Biochem Biophys. 2013;67(2):567–74.
132. Kopf J, Petersen A, Duda GN, Knaus P. BMP2 and mechanical loading
cooperatively regulate immediate early signalling events in the BMP pathway.
BMC Biol. 2012;10:37.
133. Schwarz C, Wulsten D, Ellinghaus A, Lienau J, Willie BM, Duda GN.
Mechanical load modulates the stimulatory effect of BMP2 in a rat nonunion
model. Tissue Eng Part A. 2013;19(1–2):247–54.
134. Lai CF, Cheng SL. Alphavbeta integrins play an essential role in BMP-2
induction of osteoblast differentiation. J Bone Miner Res. 2005;20(2):330–40.
135. Holguin N, Brodt MD, Silva MJ. Activation of Wnt signaling by
mechanical loading is impaired in the bone of old mice. J Bone Miner Res.
2016;31(12):2215–26.
136. Bakker AD, Kulkarni RN, Klein-Nulend J, Lems WF. IL-6 alters
osteocyte signaling toward osteoblasts but not osteoclasts. J Dent Res.
2014;93(4):394–9.
137. Sanchez C, Gabay O, Salvat C, Henrotin YE, Berenbaum F. Mechanical
loading highly increases IL-6 production and decreases OPG expression by
osteoblasts. Osteoarthr Cartil. 2009;17(4):473–81.
138. Hao ZC, Ma YY, Wu J, Li XX, Chen HL, Shen JF, et al. Osteocytes
regulate osteoblast differentiation and osteoclast activity through Interleukin-6
under mechanical loading. RSC Adv. 2017;7(79):50200–9.
139. Metzger CE, Brezicha JE, Elizondo JP, Narayanan SA, Hogan HA,
Bloomfield SA. Differential responses of mechanosensitive osteocyte proteins
in fore- and hindlimbs of hindlimb-unloaded rats. Bone. 2017;105:26–34.
1/16/20, 2:56 PMe.Proofing
Page 39 of 45https://eproofing.springer.com/journals_v2/printpage.php?token=t6UJMSWWIEq7xkPi7P6HHghsaQhfr0zzytCvR1mmCKY
https://doi.org/10.1016/j.bone.2017.08.002 .
140. Kaneshiro S, Ebina K, Shi K, Higuchi C, Hirao M, Okamoto M, et al. IL-
6 negatively regulates osteoblast differentiation through the SHP2/MEK2 and
SHP2/Akt2 pathways in vitro. J Bone Miner Metab. 2014;32(4):378–92.
141. Hu K, Olsen BR. Osteoblast-derived VEGF regulates osteoblast
differentiation and bone formation during bone repair. J Clin Invest.
2016;126(2):509–26.
142. Liu C, Zhang X, Wu M, You L. Mechanical loading up-regulates early
remodeling signals from osteocytes subjected to physical damage. J Biomech.
2015;48(16):4221–8.
143. Dumas V, Perrier A, Malaval L, Laroche N, Guignandon A, Vico L, et al.
The effect of dual frequency cyclic compression on matrix deposition by
osteoblast-like cells grown in 3D scaffolds and on modulation of VEGF variant
expression. Biomaterials. 2009;30(19):3279–88.
144. de Castro LF, Maycas M, Bravo B, Esbrit P, Gortazar A. VEGF receptor 2
(VEGFR2) activation is essential for osteocyte survival induced by
mechanotransduction. J Cell Physiol. 2015;230(2):278–85.
145. Yuan Y, Zhang LL, Tong XY, Zhang M, Zhao YL, Guo JM, et al.
Mechanical stress regulates bone metabolism through microRNAs. J Cell
Physiol. 2017;232(6):1239–45.
146. Iwawaki Y, Mizusawa N, Iwata T, Higaki N, Goto T, Watanabe M, et al.
MiR-494-3p induced by compressive force inhibits cell proliferation in
MC3T3-E1 cells. J Biosci Bioeng. 2015;120(4):456–62.
147. •• Zuo B, Zhu J, Li J, Wang C, Zhao X, Cai G, et al. microRNA-103a
functions as a mechanosensitive microRNA to inhibit bone formation through
targeting Runx2. J Bone Miner Res. 2015;30(2):330–45. Reported
1/16/20, 2:56 PMe.Proofing
Page 40 of 45https://eproofing.springer.com/journals_v2/printpage.php?token=t6UJMSWWIEq7xkPi7P6HHghsaQhfr0zzytCvR1mmCKY
mechanosensitive miR103a as a negative regulator of osteogenesis.
Mechanical unloading enhances expression of miR103a in vitro and in vivo.
Pretreatment with antagomir-103a partly rescues the osteoporosis caused
by mechanical unloading.
148. Zeng Q, Wang Y, Gao J, Yan Z, Li Z, Zou X, et al. miR-29b-3p regulated
osteoblast differentiation via regulating IGF-1 secretion of mechanically
stimulated osteocytes. Cell Mol Biol Lett. 2019;24:11.
149. Hemmatian H, Bakker AD, Klein-Nulend J, van Lenthe GH. Aging,
osteocytes, and mechanotransduction. Curr Osteoporos Rep. 2017;15(5):401–
11.
150. Sapir-Koren R, Livshits G. Is interaction between age-dependent decline
in mechanical stimulation and osteocyte-estrogen receptor levels the culprit for
postmenopausal-impaired bone formation? Osteoporos Int. 2013;24(6):1771–
89.
151. Aguirre JI, Plotkin LI, Gortazar AR, Millan MM, O'Brien CA, Manolagas
SC, et al. A novel ligand-independent function of the estrogen receptor is
essential for osteocyte and osteoblast mechanotransduction. J Biol Chem.
2007;282(35):25501–8.
152. Lee KC, Jessop H, Suswillo R, Zaman G, Lanyon LE. The adaptive
response of bone to mechanical loading in female transgenic mice is deficient
in the absence of oestrogen receptor-alpha and -beta. J Endocrinol.
2004;182(2):193–201.
153. Sugiyama T, Galea GL, Lanyon LE, Price JS. Mechanical loading-related
bone gain is enhanced by tamoxifen but unaffected by fulvestrant in female
mice. Endocrinology. 2010;151(12):5582–90.
154. Bakker AD, Klein-Nulend J, Tanck E, Heyligers IC, Albers GH, Lips P, et
al. Different responsiveness to mechanical stress of bone cells from
1/16/20, 2:56 PMe.Proofing
Page 41 of 45https://eproofing.springer.com/journals_v2/printpage.php?token=t6UJMSWWIEq7xkPi7P6HHghsaQhfr0zzytCvR1mmCKY
osteoporotic versus osteoarthritic donors. Osteoporos Int. 2006;17(6):827–33.
155. Sankardas PA, Lavu V, Lakakula B, Rao SR. Differential expression of
periostin, sclerostin, receptor activator of nuclear factor-kappaB, and receptor
activator of nuclear factor-kappaB ligand genes in severe chronic periodontitis.
J Investig Clin Dent. 2019;10(1):e12369.
156. Chatzopoulos GS, Mansky KC, Lunos S, Costalonga M, Wolff LF.
Sclerostin and WNT-5a gingival protein levels in chronic periodontitis and
health. J Periodontal Res. 2019;54(5):555–65.
157. McDonald MM, Delgado-Calle J. Sclerostin: an emerging target for the
treatment of cancer-induced bone disease. Curr Osteoporos Rep.
2017;15(6):532–41.
158. Galea GL, Lanyon LE, Price JS. Sclerostin’s role in bone’s adaptive
response to mechanical loading. Bone. 2017;96:38–44.
159. Liao HW, Huang TH, Chang YH, Liou HH, Chou YH, Sue YM et al.
Exercise alleviates osteoporosis in rats with mild chronic kidney disease by
decreasing sclerostin production. Int J Mol Sci. 2019;20(8).
160. Spatz JM, Ellman R, Cloutier AM, Louis L, van Vliet M, Suva LJ, et al.
Sclerostin antibody inhibits skeletal deterioration due to reduced mechanical
loading. J Bone Miner Res. 2013;28(4):865–74.
161. Stegen S, Stockmans I, Moermans K, Thienpont B, Maxwell PH,
Carmeliet P, et al. Osteocytic oxygen sensing controls bone mass through
epigenetic regulation of sclerostin. Nat Commun. 2018;9:2557.
162. Riddle RC, Leslie JM, Gross TS, Clemens TL. Hypoxia-inducible factor-
1alpha protein negatively regulates load-induced bone formation. J Biol Chem.
2011;286(52):44449–56.
1/16/20, 2:56 PMe.Proofing
Page 42 of 45https://eproofing.springer.com/journals_v2/printpage.php?token=t6UJMSWWIEq7xkPi7P6HHghsaQhfr0zzytCvR1mmCKY
163. Bergstrom I, Isaksson H, Koskela A, Tuukkanen J, Ohlsson C, Andersson
G, et al. Prednisolone treatment reduces the osteogenic effects of loading in
mice. Bone. 2018;112:10–8.
164. Lionikaite V, Henning P, Drevinge C, Shah FA, Palmquist A, Wikstrom P,
et al. Vitamin a decreases the anabolic bone response to mechanical loading by
suppressing bone formation. FASEB J. 2019;33(4):5237–47.
165. Parajuli A, Liu C, Li W, Gu X, Lai X, Pei S, et al. Bone’s responses to
mechanical loading are impaired in type 1 diabetes. Bone. 2015;81:152–60.
166. Seref-Ferlengez Z, Maung S, Schaffler MB, Spray DC, Suadicani SO, Thi
MM. P2X7R-Panx1 complex impairs bone mechanosignaling under high
glucose levels associated with type-1 diabetes. PLoS One.
2016;11(5):e0155107.
167. Tan SD, Kuijpers-Jagtman AM, Semeins CM, Bronckers AL, Maltha JC,
Von den Hoff JW, et al. Fluid shear stress inhibits TNFalpha-induced osteocyte
apoptosis. J Dent Res. 2006;85(10):905–9.
168. Kulkarni RN, Bakker AD, Everts V, Klein-Nulend J. Mechanical loading
prevents the stimulating effect of IL-1beta on osteocyte-modulated
osteoclastogenesis. Biochem Biophys Res Commun. 2012;420(1):11–6.
169. Liao C, Cheng T, Wang S, Zhang C, Jin L, Yang Y. Shear stress inhibits
IL-17A-mediated induction of osteoclastogenesis via osteocyte pathways.
Bone. 2017;101:10–20.
170. Pathak JL, Bravenboer N, Verschueren P, Lems WF, Luyten FP, Klein-
Nulend J, et al. Inflammatory factors in the circulation of patients with active
rheumatoid arthritis stimulate osteoclastogenesis via endogenous cytokine
production by osteoblasts. Osteoporos Int. 2014;25(10):2453–63.
171. •• Pathak JL, Bakker AD, Luyten FP, Verschueren P, Lems WF, Klein-
1/16/20, 2:56 PMe.Proofing
Page 43 of 45https://eproofing.springer.com/journals_v2/printpage.php?token=t6UJMSWWIEq7xkPi7P6HHghsaQhfr0zzytCvR1mmCKY
Nulend J, et al. Systemic inflammation affects human osteocyte-specific protein
and cytokine expression. Calcif Tissue Int. 2016;98(6):596–608. Showed the
effect of exogenous recombinant pro-inflammatory cytokines and RA-
serum on upregulation of signaling molecules and cytokine expression in
human osteocytes cultured in ex-vivo.
172. Li Z, Betts D, Kuhn G, Schirmer M, Muller R, Ruffoni D. Mechanical
regulation of bone formation and resorption around implants in a mouse model
of osteopenic bone. J R Soc Interface. 2019;16(152):20180667.
173. •• Pagnotti GM, Chan ME, Adler BJ, Shroyer KR, Rubin J, Bain SD, et al.
Low intensity vibration mitigates tumor progression and protects bone quantity
and quality in a murine model of myeloma. Bone. 2016;90:69–79. Tested the
effect of low intensity vibration (mild form of mechanical stimuli) on
multiple myeloma related bone complications. Low intensity vibration
mitigates the multiple myeloma disease progression and myeloma-induced
osteolysis and bone loss.
174. Lynch ME, Brooks D, Mohanan S, Lee MJ, Polamraju P, Dent K, et al. In
vivo tibial compression decreases osteolysis and tumor formation in a human
metastatic breast cancer model. J Bone Miner Res. 2013;28(11):2357–67.
175. Wang WB, Sarazin BA, Kornilowicz G, Lynch ME. Mechanically-loaded
breast cancer cells modify osteocyte mechanosensitivity by secreting factors
that increase osteocyte dendrite formation and downstream resorption. Front
Endocrinol. 2018;9:352.
176. Kaji H. Interaction between muscle and bone. J Bone Metab.
2014;21(1):29–40.
177. Avin KG, Bloomfield SA, Gross TS, Warden SJ. Biomechanical aspects
of the muscle-bone interaction. Curr Osteoporos Rep. 2015;13(1):1–8.
178. Jahn K, Lara-Castillo N, Brotto L, Mo CL, Johnson ML, Brotto M, et al.
1/16/20, 2:56 PMe.Proofing
Page 44 of 45https://eproofing.springer.com/journals_v2/printpage.php?token=t6UJMSWWIEq7xkPi7P6HHghsaQhfr0zzytCvR1mmCKY
Skeletal muscle secreted factors prevent glucocorticoid-induced osteocyte
apoptosis through activation of beta-catenin. Eur Cell Mater. 2012;24:197–209.
179. Kitase Y, Vallejo JA, Gutheil W, Vemula H, Jahn K, Yi J, et al. Beta-
aminoisobutyric acid, l-BAIBA, is a muscle-derived osteocyte survival factor.
Cell Rep. 2018;22(6):1531–44.
180. Huang J, Romero-Suarez S, Lara N, Mo C, Kaja S, Brotto L, et al.
Crosstalk between MLO-Y4 osteocytes and C2C12 muscle cells is mediated by
the Wnt/beta-catenin pathway. JBMR Plus. 2017;1(2):86–100.
181. Ma YV, Lam C, Dalmia S, Gao P, Young J, Middleton K, et al.
Mechanical regulation of breast cancer migration and apoptosis via direct and
indirect osteocyte signaling. J Cell Biochem. 2018;119(7):5665–75.
182. •• Ma YV, Xu L, Mei X, Middleton K, You L. Mechanically stimulated
osteocytes reduce the bone-metastatic potential of breast cancer cells in vitro by
signaling through endothelial cells. J Cell Biochem. 2018;120:7590–601.
Demonstrated the inhibitory effect of mechanically loaded osteocytes on
breast cancer metastasis to bone through the downregulation of MMP-9
and FZD4. Mechanically loaded osteocytes reduce endothelial cells
permeability and the adhesion of breast cancer cells on endothelial
monolayers.
183. Mei X, Middleton K, Shim D, Wan Q, Xu L, Ma YV, et al. Microfluidic
platform for studying osteocyte mechanoregulation of breast cancer bone
metastasis. Integr Biol (Camb). 2019;11(4):119–29.
184. Giuliani N, Rizzoli V, Roodman GD. Multiple myeloma bone disease:
pathophysiology of osteoblast inhibition. Blood. 2006;108(13):3992–6.
185. Vallet S, Filzmoser JM, Pecherstorfer M, Podar K. Myeloma bone
disease: update on pathogenesis and novel treatment strategies. Pharmaceutics.
2018;10(4).
1/16/20, 2:56 PMe.Proofing
Page 45 of 45https://eproofing.springer.com/journals_v2/printpage.php?token=t6UJMSWWIEq7xkPi7P6HHghsaQhfr0zzytCvR1mmCKY
186. Kristensen LS, Andersen MS, Stagsted LVW, Ebbesen KK, Hansen TB,
Kjems J. The biogenesis, biology and characterization of circular RNAs. Nat
Rev Genet. 2019;20(11):675–91.
187. Chen S, Zhou Y, Chen Y, Gu J. Fastp: an ultra-fast all-in-one FASTQ
preprocessor. Bioinformatics. 2018;34(17):i884–i90.
188. Gao Y, Wang J, Zhao F. CIRI: an efficient and unbiased algorithm for de
novo circular RNA identification. Genome Biol. 2015;16:4.
189. Love MI, Huber W, Anders S. Moderated estimation of fold change and
dispersion for RNA-seq data with DESeq2. Genome Biol. 2014;15(12):550.
190. Qian DY, Yan GB, Bai B, Chen Y, Zhang SJ, Yao YC, et al. Differential
circRNA expression profiles during the BMP2-induced osteogenic
differentiation of MC3T3-E1 cells. Biomed Pharmacother. 2017;90:492–9.
191. Filipowska J, Tomaszewski KA, Niedzwiedzki L, Walocha JA,
Niedzwiedzki T. The role of vasculature in bone development, regeneration and
proper systemic functioning. Angiogenesis. 2017;20(3):291–302.
192. Wei F, Xiao Y. Modulation of the osteoimmune environment in the
development of biomaterials for osteogenesis. Adv Exp Med Biol.
2018;1077:69–86.
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